The development of the different optical technologies has led to an enormous diversification of the required optical components in the last decades. Among these were classical optical components such as lenses, prisms, fibres and the like. Additionally, the requirements to their properties were strongly increasing. These properties are for example light efficiency, resolution or unconventional light transmission, but also less classical properties like thermo-shock resistant joining abilities in sockets, melting properties, suitability for secondary precision moulding and others.
These new diversified requisite profiles of the components are reflected in the newly developed optical glass types that constitute the raw material for component manufacturing. These glasses are increasingly no longer classically defined by their optical position like known optical glass families with classical composition ranges, but constitute optimized multi-component glasses for special applications.
Such “designer glasses” have to be considered very sensitive concerning their properties with regard to their compositions. Already small changes in synthesis or impurities that are due to the process conduct like for example SiO2 from quartz trough, platinum from platinum units or similar as well as small changes in process parameters like temperature, atmosphere, change in raw material form and the like have huge impact on the property profile of the glasses and render these less usable or even unusable in the worst case, while the synthesis remains unchanged.
Due to increasing environmental awareness of the industry, the market and the buyer, and also due to the improvements in legislation that are connected thereto, the number of batch components that are deployable for the implementation of the complex specification profiles of the glasses has been reduced sensitively.
Conventional refining agents have to be considered very critical with regard to this environmental aspect. These refining agents are used in order to achieve an acceptable optical inner quality as far as bubbles are concerned, while they are basically not even a part of the desired composition.
Those refining agents that are especially used for the production of glasses with highest requirements are based on chemical redox mechanisms of polyvalent components like for example arsenic and antimony oxide. After arsenic trioxide has been banned for years, the respective antimony component is more and more discredited which is among other reasons due to the transmission lowering effect at the blue spectral edge.
A further disadvantage of conventional refining agents is that these systems can only be activated at high temperatures that are for example too high for modern melting processes of new glasses with low glass transmission temperatures, also for so-called low-Tg glasses. Such systems are useless in these glasses.
Purely physical fining methods (for example evaporation, negative pressure and others) are not convincing in all glass systems, because a special concerted temperature viscosity profile is needed for their successful application, which is in conflict to applicative usage in many glass systems. Furthermore, even the physical evaporation fining process is based on more or less controllable evaporation of single components which does not contribute to the domination of such processes.
Due to the fact that conventional refining agents like polyvalent components are as such extrinsic to the synthesis and applicatively superfluous or even exerting negative influence onto the desired properties of the glasses, these components should not be used.